Gwt-gdata authentication

I'm writing an application with GWT and I found on the internet that there's a library to use easily gdata features. In particular I need to use the integration with Google Calendar. I followed the official guide on gwt-gdata site to do the authentication ( http://code.google.com/p/gwt-gdata/wiki/GettingStarted ) but unfortunately, I got an error. This is the error:

  17:59:12.463 [ERROR] [testmappa] Unable to load module entry point class testMappa.client.TestMappa (see associated exception for details)
    com.google.gwt.core.client.JavaScriptException: 
(TypeError): $wnd.google.accounts is undefined
     fileName: http://127.0.0.1:8888
     lineNumber: 29
     stack: ("http://www.google.com/calendar/feeds/")@http://127.0.0.1:8888:29
    connect("http://127.0.0.1:8888/TestMappa.html?gwt.codesvr=127.0.0.1:9997","`gL1<a3s4B&Y{(Ci","127.0.0.1:9997","testmappa","2.0")@:0
    ((void 0),"testmappa","http://127.0.0.1:8888/testmappa/")@http://127.0.0.1:8888/testmappa/hosted.html?testmappa:264
    z()@http://127.0.0.1:8888/testmappa/testmappa.nocache.js:2
    (-2)@http://127.0.0.1:8888/testmappa/testmappa.nocache.js:8
        at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:195)
        at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:120)
        at开发者_运维知识库 com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:507)
        at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:264)
        at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91)
        at com.google.gwt.accounts.client.User.login(User.java)
        at testMappa.client.TestMappa.onModuleLoad(TestMappa.java:68)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at com.google.gwt.dev.shell.ModuleSpace.onLoad(ModuleSpace.java:369)
        at com.google.gwt.dev.shell.OophmSessionHandler.loadModule(OophmSessionHandler.java:185)
        at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:380)
        at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:222)
        at java.lang.Thread.run(Thread.java:637)

I'm not able to understand the reason of this error. My code is simply:

    String scope = "http://www.google.com/calendar/feeds/";

    User.login(scope);

And as far as I know it should work as it is. I don't know what to do and I'm here to ask how to solve this problem and if I can directly use gdata native java library, but I believe this other thing is not possible to be done for client-side gwt code (since the code is going to be converted to javascript).

Thank you.

---

The two lines of code you pasted above should actually come within the run method like this -

if (GData.isLoaded(GDataSystemPackage.CALENDAR)) {
   Window.alert("Package is loaded");
} else {
   GData.loadGDataApi("MyApiKey",
      new Runnable() {
        public void run() {
             String scope = "http://www.google.com/calendar/feeds/";
             User.login(scope);
             //remaining code comes in here. you may create a new method
             //and call it from here.
        }
      },
      GDataSystemPackage.CALENDAR);
}

If you don't load the GData api code, you are likely to get the javascript error that you pasted.